Primary HIV health care clinicians and behavioral interventionists are unable to provide quality care to many HIV-infected adolescents because of difficulties, often related to substance use or mental health disorders, of engaging them in care, retaining them in behavioral interventions, and maintaining their adherence with treatment plans. The proposed longitudinal multi-site study will examine the relationships between substance use, mental health disorders, and other impediments to engagement in care for HIV-infected adolescent females, and suggest ways to promote adherence and retention in treatment, care, and prevention programs. Groundwork for the current study has been laid by the REACH Project a five-year observational study of HIV disease progression and co-morbidity in adolescents. The ATN, collaborative network of clinical (adolescent medicine) sites will provide the infrastructure for the current study. Specific aims are 1) to explore, using ethnographic methods, the inter-relationships between substance use, mental health, network substance use and other network influences, and engagement in care of HIV-infected adolescent females; 2) to determine how drug use and mental health directly and inter-actively affect engagement in care, controlling for attitudes about HIV and related health care and skills; 3) to determine how drug use among members of HIV-Infected adolescent females' social networks effects adolescent females' engagement in care, controlling for motivation and for network attitudes about HIV and related health care; 4) to determine how networks impact HIV-positive adolescent females' drug use and possible transition to injection drug or crack use and sex exchanges. The proposed project focuses on index adolescent females (n=200) and members of their kin (n=200-400) and peer networks (n=200-800) attending ATN clinical sites in Miami, New York, and Los Angeles. Qualitative and quantitative data collection methods will be used. Formal psychiatric testing with the DISC and urine drug testing will also be conducted with index participants. Interviews with index participants will be conducted every six months for 18 months and with kin and peer network participants at baseline and one year.